Flexible shaft with a helically wound data cable supporting a smooth outer sleeve for eddy current probe

ABSTRACT

A flexible shaft for use with an eddy current probe includes a flexible outer sleeve enclosing an electrically conducting coaxial cable helically coiled around a central braided wire. The braided wire is functionally incompressible and inextensible to sustain compressive forces derived from pushing the shaft through a pipe. The outer sleeve is longitudinally even accepting rollers of a pusher mechanism frictionally engaging the outer sleeve to advance the shaft without damage to the shaft as a spin motor engages the shaft to rotate the shaft as the pusher mechanism drives the probe into the pipe.

BACKGROUND

[0001] 1. Field of the Invention

[0002] This invention relates to shafts for eddy current probes and, specifically, to a flexible shaft with a smooth, protective outer sleeve for moving an eddy current probe through a pipe.

[0003] 2. Prior Art

[0004] It is known to have an eddy current probe for remotely obtaining nondestructive measurements of the integrity of tubes in nuclear steam generators and heat exchangers. The eddy current probe is pushed through a tube or pipe by a flexible shaft to which it is attached on the shaft lead, or distal end, the shaft extending from the probe to a data recorder with data cables running along the shaft. As the shaft impels the probe into the pipe, the probe measures the pipe along the pipe length, transmitting probe measurement data through cables along the shaft.

[0005] Because the nuclear industry heat exchanger pipes have a tight bend radius, typically less than 2 inches, it has been difficult to inspect them because of the inflexibility of conventional shaft materials. Without the capability of negotiating tight-radii bends, it becomes impossible to perform a full examination of the pipes from one pipe end to another, requiring multiple passes through the pipe from different pipe access locations. Completing a full pipe measurement then results in increased inspection time, increased exposure to personnel setting up the measurement equipment, and increased damage to measurement equipment.

[0006] Flexible shafts designed to protect data cables and sustain compressive forces of pushing have been tried with less than satisfactory results. The shafts typically have a structure that allows them to bend within a curved pipe and provide for data cables running with the shaft. The cables are often expensive to produce and cumbersome to use, resulting in extended inspection time and radiological exposure to personnel. Typically, the shaft outer structure also is incompatible with a probe pusher/puller device commonly used to insert the probe in a pipe. The probe pusher comprises a reel and one or more sets of opposing rollers between which the shaft passes. The motor-driven rollers engage the shaft and rotate to urge the shaft forward, unwrapping the shaft from around the reel. As the rollers engage the shaft with sufficient force to impel the shaft the rollers often damage the shaft structure.

[0007] There exist eddy current probes that are designed to rotate within a pipe causing drive and pickup coils to rotate with the rotating probe. Shafts are designed that can rotate the probe as the shaft pushes the probe along the pipe. Heretofore, such shafts have comprised an uneven outer surface susceptible to damage by engaging probe shaft pushers. It is required that a spinning motor rotate the shaft as the rollers drive the shaft into a pipe. However, the uneven shafts able to simultaneously rotate and push the probe have been destroyed in the rollers of the probe pusher.

[0008] It is a first object of the invention to provide a shaft for an eddy current probe that is not damaged by a probe pusher as the shaft is driven into a pipe. It is a second object that the shaft be rotatable by a spin motor as the probe pusher drives the shaft into the pipe without damage to the shaft. It is a third object that the shaft be sufficiently flexible to negotiate tight bends in pipes yet able to sustain compressive forces without buckling as it is pushed through the pipe.

SUMMARY OF THE INVENTION

[0009] These objects are achieved in a flexible shaft with an outer sleeve that encloses an inner shaft structure. The outer sleeve is flexible to allow necessary bending while uniformly smooth and sufficiently rigid to protect the shaft from side forces of probe pusher rollers. In addition to the measure of rigidity provided by the outer sleeve, resistance to side forces is also provided by the internal structure of the shaft as the outer sleeve broadly contacts and distributes side forces along the shaft internal structure.

[0010] The bendable outer sleeve is made of a lubric material, such as nylon, to facilitate sliding in a pipe and is generally thin-walled to facilitate bending and hence unable to sustain compressive forces of pushing. However, the outer sleeve may be enclosed around a prior eddy current probe shaft to add protection from damage from the probe pusher, therein preserving the functionality or advantage that might be offered by that prior shaft.

[0011] For simplicity and cost, ideally the shaft consists of its minimum essential elements: data cables enclosed by the outer sleeve together with a simple additional element that can sustain the compressive forces of pushing, reducing cost and adding reliability. In combination with the outer sleeve, a simplified inner structure includes comprise data cables and a braided wire cable, typically of steel or brass as an axial core, that is bendable in off axis movement in yaw and pitch but inflexible axially. Similar braided wire cables are used in automotive speedometer cables, motorcycle clutch cables, and bicycle brake cables. Such a cable is flexible yet does not buckle under longitudinal compression forces. Over long cable lengths, the unconstrained wire cable may curl or coil but when closely confined within the outer sleeve there is inadequate space for it to do so. Instead, under compressive load, that is, when pushed from an end by a shaft pusher or otherwise, the wire cable bends to a pipe being tested, but the wire cable cannot buckle within the outer sleeve when the wire cable and the outer sleeve fill a substantial portion of the pipe.

[0012] The data cables typically comprise coaxial cables helically coiled around the braided wire cable spacing the braided wire cable uniformly from the outer cable and preventing collapse of the shaft. A lubric sheath, such as a Teflon tube, surrounds the coaxial cable and braided wire shaft defining a shaft inner structure within the outer sleeve.

[0013] For purposes herein, the term “braided” is meant to include braided, woven, interlaced, twisted and all other forms of combining a plurality of small wires of little physical strength into a cable of increased tensile and compressive strength that has high deformation thresholds under strain or stress (push or pull) forces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a side cut-away view of the flexible shaft with a probe attached.

[0015]FIG. 2 is an end view of the flexible shaft of FIG. 1 along the transverse section line 2-2.

[0016]FIG. 3 is a cross-sectional view of an outer sleeve around an arbitrary eddy current probe shaft.

[0017]FIG. 4 is representative view of a flexible woven wire shaft.

[0018]FIG. 5 is a side cross-sectional view of a shaft pusher with a reel used for transporting the shaft, and an unreeled shaft rotated by a spin motor as the shaft is engaged by rollers of the shaft pusher and driven through a tubular guide to a curved pipe and into the pipe

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] The flexible shaft 5 for an eddy current probe 100 that is secured to a shaft lead end 6 comprises a protective outer sleeve 10 that closely fits around a shaft inner structure 12. The outer sleeve 10 comprises a wall 14 with an outer surface 16 that is longitudinally smooth such that rollers 110 from a shaft pusher 112 roll evenly on the outer sleeve 10 while a spin motor 111 simultaneously rotates the shaft as it moves through the shaft pusher 112. The outer sleeve 10 though flexible in bending around a curved pipe 114 is sufficiently rigid itself or when supported by the shaft inner structure 12 to sustain side forces of the rollers 1 10 without collapse. With support from the shaft inner structure, it can be more flexible yet retain strength sufficient to distribute side forces from the rollers 110 not fully resisted by the outer sleeve along the shaft inner structure 12 sufficiently so the shaft inner structure is not damaged.

[0020] The outer sleeve 10 can be effectively used over many shafts of various designs to provide similar protection from shaft pullers and generally to protect an arbitrary shaft 116 from hostile environments. The arbitrary shaft when covered by the outer sleeve 10 becomes the shaft inner structure 12, able to sustain compressive forces from pushing the shaft and oppose side forces from the shaft pusher as distributed by the outer sleeve.

[0021] To sustain compressive forces of pushing, a braided wire cable 18 is axial in the inner shaft structure in lieu of prior cable structures 116. An electrically conducting coaxial cable 20 is wound tightly on the wire cable 18 to provide electrical communication from the eddy current probe. The coaxial cable 20 is wound in a helix with winds spaced apart to facilitate bending of the braided wire cable 18. Thus wound, each small segment of the coaxial cable is effectively transverse to the shaft and therefore essentially does not flex when the shaft bends, which bending otherwise characteristically strains the insulation of the coaxial cable and compromises the integrity of data transmitted on the coaxial cable if the cable were to run parallel with the shaft and bend with the shaft.

[0022] Tape (not shown) around the coaxial cable 20 and braided wire cable 18 commonly holds the coaxial cable 20 in place around the braided wire cable 18 in combining to form the shaft inner structure 12. The shaft inner structure 12 closely fits in the outer sleeve 10. A lubric sheath 22 encloses the shaft inner structure 12 within the outer sleeve 10 reducing friction between the shaft inner structure 12 and the outer sleeve 10.

[0023] Helical wounds of the coiled coaxial cable 20 serve not only as the electrical signal conductor but also as a spacer maintaining a constant distance between the braided wire cable 18 and the outer sleeve 10. The braided wire cable 18 therefore remains constrained, centered in the outer sleeve 10 by the coaxial cable 20, the constraining structure further preventing the braided wire cable 18 from buckling under compressive forces of pushing, maintaining the integrity of the shaft. The lubric sheath 22 around the coaxial cable 18 and in contact with the bendable outer sleeve 10 reduces friction and prevents wear between the coaxial cable 18 and the outer sleeve 10.

[0024] Because the flexible shaft 5 is intended to operate in an adverse environmental condition, the outer sleeve 10 is sealed on each end by end caps 24 and 26 fully encapsulating the shaft inner structure 12. The end caps also constrain relative longitudinal movement of the sheath 22 and braided wire cable 18 and coaxial cable 20 within the tube. Otherwise, the outer sleeve 10 and sheath 22 are unattached to permit unimpeded relative movement inherent in bending. The coaxial cable 20 passes through the end caps 24 and 26 for connection to electrical connectors on shaft ends 6 and 8. 

Having described the invention, what is claimed is:
 1. A flexible shaft for moving a measuring device on a shaft lead end through a pipe, the improvement in the shaft comprising, a flexible outer sleeve running continuously between the measuring device and a shaft tail end, an inner core flexible in bending but inflexible longitudinally in sustaining compression forces that are derived from pushing the shaft through the pipe without deformation, an electrically-conducting cable running with the inner core inside the outer sleeve.
 2. The flexible shaft of claim 1 wherein the outer sleeve comprises a longitudinally even wall surface such that the shaft passes smoothly through rollers of a shaft pusher.
 3. The flexible shaft of claim 1 wherein the inner core comprises a braided wire cable.
 4. The flexible shaft of claim 3 wherein the electrically-conducting cable is helically wound around the inner core forming a longitudinally incompressible and inextensible shaft inner structure within the flexible outer sleeve.
 5. The flexible shaft of claim 4 wherein winds of the cable are spaced apart longitudinally along the wire core.
 6. The flexible shaft of claim 4 wherein the helically wound cable spaces the wire core from the outer sleeve maintaining the wire core central within the outer sleeve and preventing the wire core from buckling within the outer sleeve.
 7. The flexible shaft of claim 4 further including a lubric liner around the inner structure providing a reduced friction interface between the shaft inner structure and the outer sleeve.
 8. The flexible shaft of claim 4 further comprising end caps at each shaft end sealing the shaft inner structure within the outer sleeve and constraining longitudinal movement of the helically wound electrically-conducting cable and inner core within the outer sleeve.
 9. The flexible shaft of claim 8 wherein the cable passes through the end caps with the end caps centering the braided wire cable in the outer sleeve.
 10. An eddy current probe attached to a flexible shaft lead end, adapted to be driven into a pipe for remote nondestructive testing of the integrity of the pipe, an electrically-conducting cable running from the probe through the shaft to a shaft tail end, the improvement in the flexible shaft comprising, a flexible outer sleeve with a longitudinally even outer surface, a braided wire cable flexible in bending movement but incompressible and inextensible longitudinally in sustaining compression forces that are derived from pushing the shaft through the pipe without deformation, the electrically-conducting cable helically wound on the wire cable in spacing the wire cable from the outer sleeve maintaining the wire cable central within the outer sleeve and preventing the wire cable from buckling within the outer sleeve, the electrically-conduction cable and the wire cable forming an shaft inner structure within the flexible outer sleeve.
 11. The probe and shaft of claim 10 further comprising a sheath around the shaft inner structure and within the outer sleeve.
 12. The probe and drive shaft of claim 10 further comprising end caps at each shaft end sealing the shaft inner structure within and constraining longitudinal movement of shaft members within the outer sleeve.
 13. A flexible shaft with distal and proximal ends comprising, a flexible outer sleeve smooth throughout its outer surface and continuous without surface interruptions between tube proximal and distal ends, a flexible wire core able to sustain compression forces that are derived from pushing the shaft from its proximal end without deformation, an electrically-conducting coaxial cable helically wound tightly on the wire core wherein winds of the cable are spaced apart longitudinally along the flexible wire core, the helically wound cable functionally comprising a spacer between the wire core and the outer sleeve that maintains the wire core central within the outer sleeve preventing the wire core from buckling within the outer sleeve.
 14. The flexible shaft of claim 13 further including a sheath within the outer sleeve around the electrically-conducting coaxial cable and wire core comprising a reduced friction interface to the outer sleeve.
 15. The flexible shaft of claim 13 wherein the wire core comprises a braided wire cable.
 16. The flexible shaft of claim 13 further comprising end caps at each shaft end sealing the electrically-conducting coaxial cable and wire core within against potential hostile environmental elements and constraining longitudinal movement of shaft members and centering the wire core within the outer sleeve.
 17. For an eddy current shaft including electrically-conducting data cables along the shaft running from an eddy current probe on the shaft lead end, a method of rotating the eddy current probe on the drive shaft while simultaneously pushing the probe through a pipe, comprising the following steps: a. Enclosing the probe drive shaft with a flexible outer sleeve longitudinally even along its outer surface such that the shaft pusher rollers engaging the shaft do not damage it; b. Engaging the drive shaft with motorized shaft pusher rollers to drive the shaft into the pipe; c. Engaging the drive shaft with a spin motor to rotate the shaft as it is being driven through the shaft pusher rollers and into the pipe.
 18. The method of claim 17 wherein the probe drive shaft comprises, a flexible outer sleeve with a longitudinally even outer surface in accordance with step a. and wherein the probe drive shaft further comprises, a braided wire cable flexible in bending movement but incompressible and inextensible longitudinally in sustaining compression forces that are derived from pushing the shaft through the pipe without deformation, the electrically-conducting cable helically wound on the wire cable in spacing the wire cable from the outer sleeve maintaining the wire cable central within the outer sleeve and preventing the wire cable from buckling within the outer sleeve. 